PART L] 
Mallei: Geological Notes. 
33 
descent from tlie open and cultivated Hazaribagh plateau to the Gangetic plains. This 
broken interval varies very much in breadth; in the south-west corner of sheet 8 we have 
Sidwatand and Bishanpur respectively on the plateau and alluvium and separated by 
less than a kos, whilst from Simmeria some fifteen miles must be crossed before the 
alluvium comes in sight along the northern base of the Mahabar hills. 
Only two prominent groups of stratified rock are present: the metamorphic composed 
mainly of gneiss, with runs of hornblende rock, and the submetamorphic* which is made up 
almost entirely of mica-scliists and quartzites, with some hornblendic bands. It is scarcely 
necessary to say that the quartzites and the more granitiform varieties of gneiss form tho 
highest and most imposing masses of hill, e. g., the Bhiaura and Mahabar ranges, 
Durbasha and Maramoko Hills, whilst instances are not uncommon in which the lines of 
drainage have been scooped out of the softer schists, as in the western part of sheet 8. 
Metamobphics. —Lithologically the gneiss presents few characteristics differing from 
the ordinary ones which have been so often described elsewhere. The actual gneiss itself is 
usually composed of felspar having commonly a red color, although sometimes white, quartz, 
and uniaxial mica in small dark green or black scales. Hornblende rock and schist are 
very abundant, varying in texture from a compact stony variety to one in which the 
foliation is very prominent. Subordinate runs of mica-schist also occur, some of which 
are composed of a mixture of black mica and hornblende with quartz, others of silvery 
mica with quartz; the latter variety is similar in appearance to some of the mica-schists 
of the submetamorphic series, although clearly interbanded with and passing into the 
gneiss. 
Seldom are more perfect examples of the dome-shaped form of hill into which the gneiss 
sometimes weathers to be found than in the present area. Two cases are more especially 
prominent; tho hills which run along the north side of the Bhiaura range and those which 
internally fringe the quartzite ridge north of Gawan. In the former instance the domes 
extend from Belchaki eastwards to north of Dhubni, the rock throughout being a very 
homogeneoust compound (viewed on the large scale) of white felspar, quartz and black mica, 
containing also ill-formed porphyritic crystals of similar felspar. Nearly vertical foliation 
is almost everywhere clearly marked, even on the smooth rounded faces of the hills, running 
parallel to the quartz ridge on the south. In the previous notice of these rocks already 
alluded to, while the foliated character of the rock forming the Belchaki domes, and the 
absence of dykes l'amifying from it into the adjacent quartzite, is noticed, the possibility of 
its being, notwithstanding, of a truly granitic character is suggested, partly on stratigra- 
phical grounds and partly from the appearance of reaction of the rock in question and the 
quartzite on each other. My own more detailed examination, however, has led me to regard 
it as belonging to the metamorphic series. It certainly is more homogeneous on the large 
scale than the mass of the gneissose rocks; it does not include subordinate bands of other 
rocks such as hornblende or mica-schist. I think, however, that this is due, not to the homo¬ 
geneous and the mixed rocks being distinct in origin, but to tho fact (as 1 take it) that 
homogeniety is a necessary element in the production of the domes, and hence that it is only 
such portions of the gneiss as possess this homogeniety that weather into domes. The 
gneiss north-west of Churki for instance, and again at Pokriamo, is itself exactly of tho B61- 
chaki type, but it is interbanded with layers and beds of hornblende schist, and in neither 
case have prominent domes been formed. 
* The prefix ' sub' is used here, as in previous papers in these volumes in the same connection, to denote an 
inferior degree of metamorphisin, and has no reference to the stratigraphical position of the rocks in question. 
t In the valley south of Bdlcliaki there is a low hillock formed of what I take to be hornblende rock, 
although possibly trappean. This is the only exception I have observed, and it is in the valley between the domes, 
not in the domes themselves. 
